1. Field of the Invention
This invention relates to the field of electroanalytical chemistry, and more particularly to the field of electrolytic and electroless deposition of metal on a substrate.
2. Background of the Invention
Metal plating is of interest to the electronic industry because of the high cost of many metals, which for reasons of economy requires their use in the form of thin film plated on other less costly metals or on nonconducting substrates. The metallurgical properties of the metal deposit, however, depend on the composition of the plating baths, as well as the plating parameters. For example, the concentration of metal ions in the plating bath affects the plating rate and the plating potential. Such parameters as these tend to influence the nature and magnitude of inclusions incorporated in the deposit. Inclusions in films are known to affect metallurgical properties such as hardness, ductility, uniformity, and bondability, among others. In order to ensure consistent performance of these metal films, it is necessary to maintain the concentration of the metal ions in the plating bath within a specified range and to accurately predict the level of metal ion concentration within that range.
In the prior art, in-situ electrochemical techniques for continuously monitoring and immediately determining the concentration of metal ions in a plating bath are unknown; however, techniques involving the removal of samples from the plating bath for ex-situ analysis have been described, but these cannot be adapted to automation, are time consuming and produce results not representative of current bath conditions, which can change rapidly and unpredictably particularly in baths where high volume throughput is occurring under manufacturing conditions. This invention describes an electrochemical technique that is capable of determining metal ion concentrations continuously and currently in a plating bath and is shown to be accurate, well within the acceptable standard for manufacturing operations.